Re: Grub on BIOS/GPT

[Pascal Hambourg]

Le 21/02/2022 à 10:11, David Ventura a écrit :
> I'm not sure how to do that; running grub-install with either a file
> or a loop device as  target gets ignored and instead targets my
> primary disk:
>
> $ grub-install -vvv /dev/loop13
> grub-install: info: executing modprobe efivars 2>/dev/null.
> grub-install: info: Looking for /sys/firmware/efi ...
> grub-install: info: ...found.
> Installing for x86_64-efi platform.

The target device is ignored because grub-install detects an EFI 
platform and defaults to install for EFI boot. You must force BIOS 
platform with --target=i386-pc.

> On top of that, I'm building a franken-disk that can boot both in
> BIOS/GPT and UEFI/GPT with a bios boot partition and Grub in the ESP.
> I'm not sure if grub-install would be confused by this, or just work.
> Do you have any suggestions for this?

I observed that some BIOS platforms won't boot if the boot flag is not 
set on a partition entry of the MBR ; conversely, some UEFI platforms 
won't boot if the boot flag is set on the GPT partition entry of the 
MBR. Workaround : create a hybrid/DOS MBR or set the boot flag on an 
empty partition entry of the MBR.